https://www.nytimes.com/2019/07/02/us/citizenship-question-census.html
Because of WHY it was being added, the negative social & fiscal ramifications of non-compliance, and the ability of the GOP to use the fear of non-citizens, legal or not, to gerrymander even more districts in their favor.
Non-citizens, legal or not, are HIGHLY RELUCTANT to call attention to themselves because they FEAR the government, often with good reason.
That translates into millions of folks hiding from the census, skewing the results BIG TIME so that federal monies for schools, colleges, roads, housing, and other services are not accurate.
PLUS, it tends to skew results to favor rural areas instead of urban cities where the vast majority of non-citizens live, thus helping the GOP (whose support is heavier in rural areas). It changes how many congressional seats each area gets and what party they are most likely to be.
IOW, it's a partisan ploy to neutralize as many as 6.5 million LEGAL non-citizens and who knows how many illegal residents in favor of the GOP.
It really has NOTHING to do with voting rights or anything of the sort as some GOP have claimed. It's completely unnecessary and Thomas Hofella's posthumous release of the details of his plan PROVES that the GOP wants it ONLY to skew results towards more GOP seats.